According to the invention, an exhaust gas purification device for an engine is provided. The device comprises: a plurality of cylinders, the cylinders being divided into at least two cylinder groups; exhaust branch pipes connected to the cylinder groups at their upstream ends, respectively; a common exhaust pipe connected to the downstream ends of the exhaust branch pipes; and a NOx catalyst positioned in the common exhaust pipe. When a sulfate contamination regeneration process for regenerating the sulfate contamination of the NOx catalyst is performed by controlling the air-fuel ratio of the exhaust gas discharged from one of the cylinder groups to a rich air-fuel ratio and controlling the air-fuel ratio of the exhaust gas discharged from the other cylinder group to a lean air-fuel ratio and a purge gas including fuel vapor is purged into an intake pipe, one of the amount of purge gas and the ratio of the amount of purge gas relative to an amount of fresh air flowing through the intake pipe is controlled on the basis of the concentration of fuel vapor in the purge gas.